1. Field of the Invention
The present invention relates to a hydraulic closing unit, particularly for injection molding machines which process plastic material. The closing unit includes a mold clamping plate which is slidably guided on guide columns between a stationary support plate and a stationary mold clamping plate. An annular main piston acts on the slidable mold clamping plate with a high mold closing force in mold closing direction. The main piston is axially slidably guided in the stationary support plate and load can be applied to both sides of the main piston. A mechanical support means acts on the main piston between the main piston and a mechanical pressure connection acting on the mechanical support means through a central pressure column.
2. Description of the Related Art
A hydraulic closing unit of the above-described type is known from German Auslegeschrift 20 19 883.
The known closing unit is constructed to be capable of carrying out with separate means the different operations, namely the closing operation, the opening operation and the sliding operation, wherein the sequence of operations is accelerated. On the other hand, the known closing unit makes it possible to carry out a hydraulic mold level compensation with a rigid guidance of the movable mold clamping plate.
However, the known closing unit has the disadvantage that the possible mold level compensation is determined by the available maximum moving distance of the annular piston minus the moving distance required for closing and opening the mold. Accordingly, in the known closing unit, the maximum moving distance of the annular piston must be dimensioned substantially greater than the moving distance required for opening and closing the mold.
French patent No. 1,275,850 discloses a hydraulic closing unit in which the work position of the cylinder for generating the mold closing force can be obtained mechanically. However, also in this case, the possible adjustment range is basically dependent upon the maximum effective operating length of the cylinder, wherein this length again must be dimensioned greater than the adjusting distance required for opening and closing the mold.